<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <meta http-equiv="X-UA-Compatible" content="IE=edge">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>预解析</title>
</head>
<body>
    <script>

          function foo1(){
              function foo2(){

              }

              var a=12;
              return foo2;
          }

          foo1()

       

    </script>
</body>
</html>